Transfer line burner system

ABSTRACT

Carbonaceous solids are heated by introducing a stream of such solids into a transfer line burner, injecting sufficient oxygencontaining gas into the burner at two or more separate points to burn a portion of the carbon and generate heat, controlling distribution of the oxygen-containing gas to maintain temperatures below the ash fusion temperature and convert carbon monoxide to carbon dioxide, and withdrawing heated solids from the burner.

United States Patent Nahas et al.

1 1 TRANSFER LINE BURNER SYSTEM [75] Inventors: Nicholas C. Nahas;Edward L. Wilson, both of Baytown, Tex.

[73] Assignee: Exxon Research and Engineering Company, Linden, NJ

[22] Filed: June 25, 1973 [21] Appl. No.: 373,554

[52] US. Cl. 48/197 R; 201/31 [51] Int. Cl.. Cl0j 3/12 [58] Field ofSearch 48/202, 206, 204, 210,

48/147 R, DIG. 4; 201/38, 9, 31; 252/373,

[56] References Cited UNITED STATES PATENTS 2.374660 5/1945 Belchetz eta1, 252/417 2,588,075 3/1952 Barr et a1 1 v 1 1 48/206 2,654,665 10/1953Phinney 1 1 1 48/206 2 667,410 1/1950 Pierce 1 1 1 48/196 2,694,62311/1954 We1ty.1r. at al. 48/197 2,729,552 1/1956 Nelson et a1 48/1972.741.549 4/1956 Russell 0. 48/206 COAL FE ED 1.0

FEED GAS STEAM STEAM Primary ExaminerS. Leon Bashore AssistantE.mminer-Peter F. Kratz Attorney, Agent, or Firm-James E. Reed [57]ABSTRACT Carbonaceous solids are heated by introducing a stream of suchsolids into a transfer line burner, injecting sufficientoxygemcontaining gas into the burner at two or more separate points toburn a portion of the carbon and generate heat, controlling distributionof the oxygen-containing gas to maintain temperatures below the ashfusion temperature and convert carbon monoxide to carbon dioxide, andwithdrawing heated solids from the burner.

5 Claims, 1 Drawing Figure PRODUCT GAS "FLUE GAS CARBON MONOXIDECUNTROLLE R 1 1 s y n 33 i TEMP.

CONTROLLER 32- [ff 30 2s 1 OXYGEN CONTAINING GAS STEA

PATENTED JUN 2 4 I575 -D PRODUCT GAS D FLUE GAS COAL FEED FEED GAS4DILUENT GAS H H G NwL U. L I m? W RN M A AOM MZ 6 M M T 2 W C C C 9 I ollllllllll J 3 7 2 1| 4 3 Q 0 3 3 3 3 n m d. g 8 7 6 3 3 3 3 2 4 9 2 JA. 5 m a n. a w. 2 m

STE AM TRANSFER LINE BURNER SYSTEM BACKGROUND OF THE INVENTION 1. Fieldof the Invention This invention relates to the heating of fluidized bedscontaining coal particles or other carbonaceous solids and isparticularly directed to coal gasification and related processes inwhich heat is generated by burning a portion of the carbonaceous solidsin a transfer-line burner.

2. Background of the Invention The production of carbon monoxide andhydrogen from steam and coal char or other carbonaceous solids is ahighly endothermic reaction. One of the more attractive methods forproviding the heat required to carry out this reaction involves the useof a fluidized bed reaction zone and a transfer-line burner. Typically,such a burner consists of a large vertical line into which a steam ofchar particles or other carbonaceous solids is continuously introducedfrom the reaction zone. The carbonaceous solids are entrained by gas andcarried upwardly through the burner to an overhead separation zone wheregases and entrained solids are separated. The unburned solids are thenreturned to the reaction zone. Sufficient heat to maintain the fluidizedbed at the desired reaction temperature is generated by introducing airnear the lower end of the burner. The amount of air employed isregulated so that only part of the solids are burned to form carbondioxide. Ash and fines are carried overhead from the separation zone andcan be removed by scrubbing or other conventional treatment before theflue gas is discharged.

Although the use of a transfer-line burner as described above hasimportant advantages over other heat generating systems, experience hasshown that the combustion taking place in the burner is difficult tocontrol. The oxygen present in the input gas stream reacts with the hotchar or other solids at rates such that localized overheating may takeplace near the injection nozzles. If the transient, localizedtemperature rise ex ceeds the ash fusion temperature, plugging problemsand other difficulties may be encountered. In addition, studies haveshown that the combustion efficiency in such burners is often poor andthat effective pollution control may pose additional problems.

SUMMARY OF THE INVENTION The present invention provides a method forcontrolling the operation of transfer-line burners used in coalgasification and similar operations which at least in part alleviatesthe difficulties outlined above. In accordance with the invention, ithas now been found that the operation of such burners can be effectivelycontrolled by injecting an oxygen-containing gas into the burner at twoor more separate points and regulating distribution of this gas tominimize ash fusion and the formation of carbon monoxide. Theoxygen-containing gas is preferably introduced at a first point near thelower end of the burner and at one or more additional points downstreamfrom the first point. The amount of oxygen introduced at the first pointwill preferably be sufficient to generate a substantial portion of theheat required to raise the solids in the burner to the desiredtemperature. The oxygen thus provided is quickly consumed in burningcarbon to form carbon dioxide. As the gaseous products and unburnedsolids move upwardly within the burner, the carbon dioxide is partiallyreduced to carbon monoxide in accordance with the reaction: CO +C 2C0.The amount of oxygen introduced downstream from the first point willpreferably be sufficient to burn substantially all of the carbonmonoxide to carbon dioxide and provide additional energy for heating theunburned solids.

It is preferred to regulate the total quantity r." air or otheroxygen-containing gas admitted to the transfer line burner by means ofthermocouples located in the reactor and a temperature controller towhich the thermocouples are connected. The temperature controlleractuates an electrically or hydraulically operated valve in the air orgas line and thus controls the amount of air or gas introduced so thatthe reactor temperature remains at the desired level. It is alsopreferred to regulate the amount of air or other oxygen-containing gasintroduced downstream from the first point by means of an electricallyor hydraulically operated valve controlled by a carbon monoxide analyzerand controller connected to the flue gas outlet from the burner. Anyincrease in the concentration of carbon monoxide in the flue gas streamwill thus be sensed by the analyzer and additional air oroxygen-containing gas will be admitted through the valve to reduce thecarbon monoxide concentration to the desired level.

The method of the invention permits substantially better control of thecombustion in transfer-line burners than has generally been obtained inthe past. The introduction of a portion of the total air or otheroxygen-containing gas near the lower end of the burner and theintroduction of additional air or gas at one or more points downstreamfrom the initial air or gas inlet reduces the likelihood of localizedoverheating and the attendant problems due to ash fusion, results inmore efficient combustion and the transfer of greater quantities of heatto the suspended solids, and makes possible substantial reductions inthe amount of carbon monoxide in the flue gases, thus reducing pollutionproblems and simplifying any later treatment of the flue gases which maybe necessary to comply with applicable pollution control regulations.These and other advantages make the method of the invention attractivefor use in a variety of different applications.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE in the drawing is aschematic flow sheet of a process for producing a methane-rich gas fromcoal in which the improved transfer-line burner system of the inventionis used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process depicted in thedrawing is one for the production of product gases of relatively highmethane content from bituminous coal, subbituminous coal, lignite, solidpetroleum residua or similar carbonaceous solids. The solid feedmaterial employed in the process, preferably a bituminous or lower rankcoal, is introduced into the system through line 10 from a suitable feedpreparation plant or storage facility not shown in the drawing. Topermit handling of the feed material in a fluidized system, the coal orother carbonaceous solid material is introduced in a finely-dividedstate, preferably less than about 8 mesh on the Tyler Screen Scale.

The system depicted in the drawing is operated at elevated pressures andhence the coal or other feed material introduced through line 10 is fedinto vessel 11,

from which it is discharged through star wheel feeder or similar device12. into line 13 at the system operating pressure or at a slightlyhigher pressure. In lieu of or in addition to this type of anarrangement, parallel lock hoppers, pressurized hoppers, or aeratedstand pipes operating in series may be employed to raise the input coalstream to the system operating pressure. The use of such devices forhandling coal and other finelydivided solids at elevated pressures hasbeen described in the patent literature and will therefore be familiarto those skilled in the art.

The solid particles admitted into the system through line 13 areentrained in a feed gas stream introduced through line l4 and fed intogasifier 15. High pressure steam or product gas may be used as the feedgas. The use of product gas is normally preferred. This gas isintroduced into the system at a pressure between about 50 and about 1000pounds per square inch gauge, depending in part upon the pressure atwhich gasifier 15 is operated and the solid feed material employed. Thefeed stream is introduced into the gasifier through a shrouded nozzleprovided with steam admitted through line 16 to keep the feed injectionnozzle at a temperature below about 600 F. and thus avoid fouling of thenozzle with agglomerating coal solids. If an agglomerating coal isemployed as the coal feed material, an injection nozzle designed topromote intimate and extremely rapid mixing of the injected coal withthe hot solids in the gasifier will normally be employed. Nozzlessuitable for this purpose have been described in the prior art.

The gasifier vessel 15 employed in the system shown in the drawingcontains a fluidized bed of char particles which are introduced into thelower part of the vessel through line 17. Steam for reacting with thechar and maintaining the particles in the fluidized state is introducedinto line 17 through line 18. Additional steam may be introduced throughline 19. The total steam rate will normally range between about 0.5 toabout 2.0 pounds of steam per pound of coal feed. The upflowing steamand char form a fluidized bed which extends upwardly above distributiongrid or similar device to a level above the point at which the coalsolids are introduced into the gasifier. The lower portion of thegasifier vessel above grid 20, indicated by reference numeral 21, servesas a steam gasification zone. Here the steam introduced through lines 18and 19 reacts with carbon in the hot char to form synthesis gas inaccordance with the reaction: H O+C H -l-CO. At the point of steaminjection near the bottom of the gasifier, the hydrogen concentration inthe gaseous phase of the fluidized bed is essentially zero. As the steammoves upwardly through the fluidized char particles. it reacts with thecarbon, and the hydrogen concentration in the gaseous phase increases.The temperature in steam gasification zone 21 will normally rangebetween about l450 and about 1800 F. The gas velocities in the fluidizedbed will generally range between about 0.2 and about 3.0 feet persecond.

The upper part of the fluidized bed in reactor vessel 15 serves as ahydrogasiflcation zone, indicated by reference numeral 22, where thefeed coal is devolatilized and a part of the volatile matter thusproduced reacts with hydrogen generated in zone 21 to produce methane asone of the principle products. The point at which the coal feed streamis introduced into the gasifier and hence the location of the steamgasification and hydrogasification zones depends primarily on theproperites of the particular coal which is employed as the feedstock.ltis generally preferred to maximize the methane yield from the gasifierand minimize the tar yield. Generally speaking, the amount of methaneproduced increases as the coal feed injection point if moved nearer thetop of the reactor. The tar, which has a tendency to foul downstreamprocessing equipment. generally increases as the coal injection point ismoved upwardly in the gasifier and decreases as the coal input point ismoved nearer the bottom of the reactor, other operating conditions beingthe same. The coal feed should generally be injected into gasifier 15 ata point where the hydrogen concentration in the gas phase is in excessof about l5 percent by volume, preferably between about 25 percent andabout 50 percent by volume. The upper surface of the fluidized bed willnormally be located at a level sufficiently above the feed injectionpoint to provide at least about 4 seconds of residence time for the gasphase in contact with the fluidized solids in hydrogasiflcation zone 22.It is preferred in general that the residence time for the gas incontact with the solid phase above the point of coal feed injection bebetween about 7 and about 20 seconds. It will be understood, of course,that the optimum hydrogen concentration at the coal injection point andgas residence time above the point of coal injection will vary withdifferent types and compositions of feed coal and with variations in thegasifier temperature, pressure, steam rate and other processingconditions. Higher rank coals normally require somewhat more severereaction conditions to obtain practical reaction rates than do coals oflower rank. Similarly, higher reactor temperatures and steam ratesnormally tend to increase the hydrogen concentration in the gas phaseand thus reduce the solids residence times required for gasification ofa given coal feed.

As indicated earlier, the temperature in gasifier 15 is normallymaintained within the range between about I450 and about i800 F. Theheat required to sustain the overall endothermic reaction taking placein the gasifier and maintain this operating temperature is provided bywithdrawing a portion of the char solids from the fluidized bed throughline 23 and passing this material into the lower end of transfer lineburner 24. Steam may be injected into line 23 in the vicinity of bendsin the line in order to promote smooth flow of the solids and avoid anydanger of clogging. Similarly, a diluent gas, flue gas for example, maybe injected through line 25 to further aid in suspending the solids andentrain them in dilute phase flow as they move upwardly through thetransfer-line burner. An oxygen-containing gas, preferably air, isintroduced into the burner through line 26 in a quantity sufficient topromote combustion of a portion of the char and thus provide the heatnecessary. The amount of air or gas introduced should be sufficient toraise the temperature of the upflowing solids stream from an initiallevel of from about l4SO to about l800 F. to a final level between about1500 and about l950 F. The particles recycled from the burner to thefluidized bed will generally be at a temperature of from about 50 to300+ F. higher than the bed temperature, preferably about 200 F. orhigher. The amount of carbon which must be burned to carbon dioxide togenerate the necessary heat and the quantity of oxygen that will berequired for this purpose will depend upon the quantity and type ofsolids being handled, the amount of diluent gas present, the combustionefficiency, the heat losses which occur, and other factors. In general,it is normally preferred to inject air at the rate of from about 0.02 toabout 0.20 pound per pound of char being circulated. If anoxygen-containing gas having a lower oxygen content than air is used,the gas injection rate will have to be increased correspondingly.

The flow rate of gas introduced through line 26 is adjusted by means ofvalve 27. This valve is actuated by a control system that in net effectmeasures the temperature in the gasifier by a device 29 such as athermocouple or pyrometer and by means of controllers in the systempositions valve 27 to hold the desired temperature. Although only onethermocouple or the like has been shown, a plurality of such devicesspaced about the inner wall of the reactor will normally be used tomonitor the temperature of the fluidized bed. In response to the inputfrom these thermocouples, the controller increases or decreased theamount of oxygencontaining gas which passes through valve 26. This inturn increases or decreases the amount of heat generated within theburner and thus permits maintaining of the fluidized bed at the requiredtemperature level. In lieu of thermocouples or pyrometers, othertemperature sensing equipment designed to monitor the bed temperaturemay be used. Such equipment may be obtained from commercial sources.

Combustion theory indicated that the oxygen introduced into contact withthe hot char particles near the lower end of the transfer-line burner isconsumed very rapidly, generally in from about 0.001 to about 0.0]second. Because of the burner length required to handle the solids froma commercial-size fluid bed reactor and the limitations on gas velocityimposed by the necessity for avoiding excessive particle attrition, thetotal residence time of the char solids in the burner will normallyrange between about 0.3 and about 5.0 seconds. The combustion gases in aconventional burner therefore remain in contact with hot char particlesfor a relatively long period of time following the generation of heatand the formation of carbon dioxide in the combustion process. As theparticles and hot gases move upwardly in the burner, a portion of thiscarbon dioxide is reduced to carbon monoxide until an equilibrium isestablished. This formation of carbon monoxide consumes heat and reducesthe overall efficiency of the combustion process taking place in thetransfer-line burner. The carbon monoxide, if not removed, alsocontributes to pollution problems and makes cleanup of the flue gasesfrom the burner more difficult. in addition, a large quantity of oxygeninjected near the lower end of the burner can produce localizedoverheating, which can result in temperatures in excess of the ashfusion temperature and lead to plugging problems and other difficulties.

To alleviate the problems referred to above, the oxygen-containing gasintroduced to the transfer-line burner through line 26 and valve 27 isinjected into the burner at two or more separate points along theburner. A portion of this gas enters the burner near the lower endthrough line 30 and multiple injection nozzles 31 spaced about theburner periphery to promote effective contact between the gas and thesolids moving upwardly through the burner. The remainingoxygencontaining gas passes upwardly through line 32 and is introducedinto the burner through one or more downstream injection lines 33, 34and 35 and the associated peripherally-spaced nozzles 36, 37 and 38. Itis generally preferred that the injection lines be spaced sufficientlyfar apart to permit consumption of substantially all of the oxygen asthe upflowing particles move between the nozzles associated with oneline and those associated with the next line. A spacing of at least 30inches in normally advantageous.

The oxygen-containing gas introduced near the upper end of the burner,through line 35, is passed through an electrically orhydraulically-operated control valve 39 which is connected to a carbonmonoxide analyzer and control unit 40 of conventional design. Such unitsare available from commercial sources. The flue gases from the burnerare sampled continuously through line 41 to operate the control unit. Ifthe carbon monoxide content of the flue gases from the burner increasesbeyond a predetermined level, the control unit opens valve 39 wider toincrease the amount of air or oxygen-containing gas introduced throughline 35 and reduces the quantity admitted upstream of line 35. Theadditional oxygen thus admitted near the upper end of the burner reactswith carbon monoxide in the gas stream to convert it into carbondioxide, thus reducing the carbon monoxide content of the gases leavingthe burner. This generates additional heat which is in part transferredto the suspended solids in the gas stream, improves the overallcombustion efficiency of the burner, and maintains the carbon monoxidein the flue gases at the desired level.

The gases and hot suspended solids leaving the upper end of thetransfer-line burner are introduced into a separation zone 42 which willnormally contain one or more centrifugal separators in which the largersolid particles are separated from the combustion gases and conductedthrough dipleg 43 back to the reactor 15. The solids are transferredfrom the dipleg into line 17, from which they are returned to thefluidized bed by means of steam introduced through line 18. Supplementalsteam may be injected into the dipleg as necessary to control the solidsflow rate and facilitate movement of the solid particles around bends inthe line. Most of the ash formed in the burner is carried overhead withthe flue gases and discharged from separation zone 42 through gas line44. Some char fines will normally also be present in the flue gases. Theash and fines can be removed from the gas stream by passing the gasesthrough additional centrifugal separators, scrubbing the gases, and thelike.

The products formed in gasifier 15 by reaction of the steam and char insteam gasification zone 21 and devolatilization of the feed coal andreaction of the volatile products with hydrogen in hydrogasificationzone 22 are carried overhead from the fluidized bed and pass through agas solids separating zone 45 where entrained solids are removed fromthe gas stream and returned to the gasifier-burner system. The productgas is taken overhead from the separation zone through line 46. This gasmay be further treated for the removal of fines and other undesirableconstituents in the conventional manner and then employed as a fuel gas.

The nature and objects of the invention can be more fully understood byconsidering the results of pilot plant tests of a transfer-line burnerand an example of a coal gasification process in which a transfer-lineburner constructed in accordance with the invention is employed.

EXAMPLE 1 Pilot plant tests were carried out with a transfer-line burnerused for the combustion of coal char particles to heat a fluidized bed.The burner was operated at a temperature of approximately l800 F. and 50pounds per square inch gauge pressure. Air was injected into the lowerend of the burner and samples of the flue gases produced were taken atthree different sampling points in the burner. The first such point waslocated 12 feet above the air injection point, the second point was feetabove the air injection nozzles, and the third point was near the upperend of the burner, 46 feet above the air injection point. The gasresidence time between the air injection nozzle and each sampling pointwas calculated and the flue gas samples at each point were analyzed todetermine the amounts of carbon dioxide and carbon monoxide present ineach sample. The results obtained are shown in the following It can beseen from the data in Table I that the gases produced in thetransfer-line burner contained significant amounts of both carbondioxide and carbon monoxide. lnitial combustion of the char followingthe introduction of oxygen-containing gas at the air injection nozzleevidently took place very rapidly so that all of the injected oxygen wasconsumed within a very short distance of the nozzle. As the gases movedupwardly through the burner, the concentration of carbon dioxidedecreased and the carbon monoxide concentration increased, indicatingthat carbon dioxide was being reduced to carbon monoxide in the presenceof the hot char. The gas residence times indicated in the table showthat this reduction of carbon dioxide takes place rapidly untilequilibrium between the carbon dioxide and the carbon monoxide isapproached or established.

The equilibrium concentrations of carbon dioxide and carbon monoxide inthe presence of carbon is a function of temperature. The relativeproportions of the two gases that will be present for a carbon dioxidepartial pressure of one atmosphere in the presence of hot carbon atvarious temperatures is shown in Table II below.

It can be seen from the values in Table ll that the equilibrium partialpressure of carbon monoxide is much greater than that of carbon dioxideat temperatures of l400 F. and higher and that, at temperaturesrepresentative of those at which most transfer-like burners normallyoperate. the amount of carbon monoxide present will therefore be greaterthan the amount of carbon dioxide if equilibrium is reached. The dataset forth in Table I tend to confirm this.

Following the tests described above, the transfer-line burner employedearlier was modified to permit the injection of supplementary air at the12 foot level. Samples of the gases generated in the burner were thentaken at the 25 foot level while operating the burner at about l800 F.and 50 pounds per square inch gauge. The amount of air introduced at theair injection nozzle near the lower end of the burner was the same as inthe earlier case. The amount of supplementary air injected at the 12foot level was varied and the gas samples recovered at the 25 foot levelwere analyzed to determine the amounts of carbon monoxide and carbondioxide present. The results obtained are set forth in Table III.

TABLE II] Effect of Supplementary Air at Second Injection PointSupplementary 0 Carbon Oxide Rates.

The data in Table lll demonstrate that the injection of small amounts ofoxygen-containing gas into the transfer-line burner at a second pointdownstream from the point at which gas was initially injected to permitcombustion of the char produced a significant reduction in the amount ofcarbon monoxide present in the gas stream and a corresponding increasein the amount of carbon dioxide present. This conversion of carbonmonoxide to carbon dioxide increases the amount of heat available forraising the temperature of the carbonaceous solids present in the gasstream, improves the combustion efficiency of the burner, and alleviatespollution control problems. In some cases these improvements may makepossible significant savings in the overall cost of the process in whichthe transfer-line burner is used.

To obtain maximum combustion efficiency in the transfer-line burner,sufficient air or other oxygencontaining gas should be injected near thetop of the burner so that essentially all of the carbon monoxide will beburned to carbon dioxide, the heat of combustion being absorbed by thesolids. The solid particles should be separated from the gas streambefore significant additional conversion of carbon dioxide to carbonmonoxide occurs. This can be accomplished by injecting sufficient air toburn all of the carbon monoxide, plus a small excess, so that the solidsare discharged from the gas stream while some oxygen is still present inthe gas. The amount of air or other oxygencontaining gas required forthe generation of sufficient heat to raise the temperature of the solidsin the gas stream to the desired level and the amount of gas required toconvert the carbon monoxide to carbon dioxide can be readily calculatedfor any particular set of transfer-line burner operating conditions.

EXAMPLE 2 This example summarizes a calculated material balance for agasification operation in which bituminous coal is converted into amethane-rich gas in a gasifier of the type shown in the drawing, heatfor the process is provided by circulating char solids through atransfer-line burner as disclosed herein, and the operation of theburner is controlled in accordance with the invention by injectingcombustion air into the burner at a first point near the lower end ofthe burner and injecting additional oxygen-containing gas into theburner downstream from the first point. The operating conditions for theprocess are set forth in the following table.

TABLE IV Thousands of Pounds] Hour CH 38 CO 1 55 C0 1 19 H 1) H 0 1 12Other 28 Total 47 1 The steam rate to the reactor is 219,000 pounds perhour and the amount of char recycled into the reactor through line 17 is8,224,000 pounds per hour.

Char is continuously withdrawn from the reactor and fed through line 22to the transfer-line burner at the Gasification Process OperatingConditions Broad Range Preferred Range Specific Example Item (All Coals)(Bituminous Coals) (Bituminous Coal) Gasifier Temperature, "F. 1450-18001500-1700 1600 Pressure. psig 50-1000 100-500 180 Steam Rate/Coal FeedRate. Lbs/Lb. 0.2-2.0 0.51.5 1.0 Steam Superficial Velocity, Ft./Sec."'0.2-2.0 0.5-1.5 0.53 Char Solids Holdup in Bed/Coal Feed Rate, Hrs.0.2-5.0 0.5-3.0 0.64 Product Gas Elfluent Rate/Coal Feed Rate.

SCF/Lh. 15-40 -30 25 Product Gas Composition, Mole "/1 CH, 0-20 5-10 8.7CO 5-40 1 5-25 20.6 C0: 0- 5-15 10.0 H, 10-50 30-40 35.5 H,O 5-50 1 5-3022.9 other 0-10 0-5 2.3 Transfer-Line Burner Char Solids InletTemperature, F. 1450-1800 1500-1700 1600 Outlet Temperature. F.1500-1950 1600-1900 1800 Outlet Pressure. psig -1000 100-500 180 CharCirculation Rate/Coal Feed Rate, LhsJLb. 10-100 10-30 20 Combustion AirRate/Char Circulation Rate.

l.hs./Lh. 0.02-0.2 0.05-0.15 0.1 Solids Residence Time. Sec. 0.1-5.00.5-1.5 1.0 Gas Superficial Velocity, FtJSec. 30-300 50-150 I 10 FlueGas Rate/Coal Feed Rate, SCF/Lb. 28 Flue Gas Composition, Mole '4 C00-10 0-2 1.7 CO, 10-25 15-22 17.2 11,0 0-20 10-15 11.6 0, 0-5 0-2 Nil N,50-90 60-80 66. 1 Other l-l0 1-5 3.4

"'At lluidind bed temperature and pressure.

In an operation carried out under the conditions listed for the specificexample in the above table, the feed rate is 410,000 pounds ofbituminous coal per hour. The ultimate analysis of the coal feed is:

Thousands of Pounds/Hour Carbon 270 Hydrogen 19 Oxygen 67 Nitrogen 4Sulphur 2 Ash 32 Water 1 6 Total 4 10 rate of 8,364,000 pounds per hour.To promote combustion of the char solids in the burner, combustion airis introduced into the burner system through line 26 and valve 27 at therate of 747,000 pounds per hour. A portion of this air is injectedthrough each of the four air inlet lines as shown. The distribution ofair between the uppermost inlet line 35 and lower inlet lines 30, 33 and34 is varied by valve 39 and controller 40 as necessary to maintain thecarbon monoxide content of the flue gas at the low level indicated inTable IV above. The flue gas taken off overhead from the burner isdischarged at the rate of 883,400 pounds per hour. This gas has thecomposition shown in Table IV and contains the listed constituents inthe following amounts:

Hot char solids separated from the flue gas stream in separation zone 32are recycled to the gasifier through line 33 at the rate of 8,322,000pounds per hour.

What is claimed is:

1. In a process wherein a solids stream consisting esgases containingcarbon monoxide are withdrawn overhead from said transfer line burner,and wherein said heated particles are separated from said combustiongases and returned to said fluidized bed reactor; the improvement whichcomprises introducing a first stream of oxygen-containing gas into saidtransfer line burner at a point near the lower end thereof in a quantitysufficient to initiate the combustion of carbon in said particles,introducing additional oxygen-containing gas into said burner at asecond point near the upper end of said burner in a quantityisufficientto burn carbon monoxide present in the combustion gases reaching saidsecond point and generate additional heat, monitoring the carbonmonoxide content of the combustion gases withdrawn from said burner,regulating the relative quantities of oxygen-containing gas introducedinto said burner at said first point and said second point in responseto changes in the carbon monoxide content of said combustion gaseswithdrawn from said burner, and

'controlling the total amount of oxygen-containing gas introduced intosaid burner in response to changes in the temperature in said fluidizedbed reactor.

2. A process as defined by claim 1 wherein said carbon monoxide contenof said combustion gases is monitored by continually sampling said gasesand analyzing the gas samples for carbon monoxide and wherein therelative amounts of oxygen-containing gas introduced at said first andsaid second points are regulated by varying the amount ofoxygen-containing gas supplied to said burner at said second point inresponse to changes in the carbon monoxide content of said gas samples.

3. A process as defined by claim 1 wherein oxygencontaining gas is alsointroduced into said burner at at least one point intermediate saidfirst and said second points.

4. A process as defined by claim 1 wherein said oxygen-containing gas isintroduced into said burner at said second point in a quantity in excessof that required to burn essentially all of the carbon monoxide reachingsaid second point.

5. A process as defined by claim 1 wherein said oxygen-containing gas isintroduced into said burner at each of said points through a pluralityof nozzles spaced about the periphery of said burner.

1. IN A PROCESS WHEREIN A SOLIDS STREAM CONSISTING ESSENTIALLY OFCARBONACEOUS PARTICLES WITHDRW FROM A FLUIDIZED BED REACTORS ISCONTACTED WITH AN OXYGEN-CONTAINING GAS IN A TRANSFER LINE BURNER TOBURN CARBON PRESENT IN SAID PARTICLES AND RAISE THE TEMPERATURE OF SAIDSTREAM, WHEREIN HEATED PARTICLES AND COMBUSTION GASES CONTAINING CARBONMONOXIDE ARE WITHDRAW OVERHEAD FROM SAID TRANSFER LINE BURNER, ANDWHEREIN SAID HEATED PARICLES ARE SEPARATED FROM SAID COMBUSTION GASESAND RETURNED TO SAID FLUIDIZED BED REACTOR; THE IMPROVEMENT WHICHCOMPRISES INTRODUCING A FIRST STREAM OF OXYGEN-CONTAINING GAS INTO SAIDTRANSFER LINE BURNER AT A POINT NEAR THE LOWER END THEREOF IN A QUANTITYSUFFICIENT TO INITATE THE COMBUSTION OF CARBON IN SAID PARTICLESINTRODUCING ADDITIONAL OXYGEN-CONTAINING GAS INTO SAID BURNER AT ASECOND POINT NEAR THE LOWER END OF SAID BURNER IN A QUANTITY SUFFICIENTTO BURN CARBON MONOXIDE PRESENT IN THE COMBUSTION GASES REACHING SAIDSECOND POINT AND GENERATE ADDITIONAL HEAT, MONITORING THE CARBONMONOXIDE CONTENT OF THE COMBUSTION GASES WITHDRAWN FROM SAID BURNER,REGULATING THE RELATIVE QUANTITIES OF OXYGEN-CONTAINING GAS INTRODUCEDINTO SAID BURNER AT SAID FIRST POINT AND SAID SECOND POINT IN RESPONSETO CHANGES IN THE CARBON MONOXIDE CONTENT OF SAID COMBUSTION GASESWITHDRAWN FROM SAID BURNER, AND CONTROLLING THE TOTAL AMOUNT OFOXYGEN-CONTAINING GAS INTRODUCED INTO SAID BURNER IN RESPONSE TO CHANGESIN THE TEMPERATURE IN SAID FLUIDIZED BED REACTOR.
 2. A process asdefined by claim 1 wherein said carbon monoxide content of saidcombustion gases is monitored by continually sampling said gases andanalyzing the gas samples for carbon monoxide and wherein the relativeamounts of oxygen-containing gas introduced at said first and saidsecond points are regulated by varying the amount of oxygen-containinggas supplied to said burner at said second point in response to changesin the carbon monoxide content of said gas samples.
 3. A process asdefined by claim 1 wherein oxygen-containing gas is also introduced intosaid burner at at least one point intermediate said first and saidsecond points.
 4. A process as defined by claim 1 wherein saidoxygen-containing gas is introduced into said burner at said secondpoint in a quantity in excess of that required to burn essentially allof the carbon monoxide reaching said second point.
 5. A process asdefined by claim 1 wherein said oxygen-containing gas is introduced intosaid burner at each of said points through a plurality of nozzles spacedabout the periphery of said burner.